Anatomy of the intrinsic hand muscles revisited: Part I. Interossei

In this article, the anatomic variations in interosseous muscle insertions are described based on a review of the literature and 14 fresh cadaver hand dissections. The findings are correlated and compared with those of a number of other investigators, and the clinical implications are discussed (i.e., in the correction of ulnar deviation in arthritis patients and in the treatment of congenital anomalies of the hand). It is concluded that descriptions of insertion sites of the intrinsic muscles have been oversimplified by previous researchers, and a number of variations are identified through the cadaver dissections. The differing and confusing nomenclature used by other investigators is discussed and simplified. The results of this study indicate that not only are there important distal insertions onto bone and the extensor apparatus, but there is also an additional insertion onto the volar plate ("assemblage nucleus"), as Zancolli reported. It was found that the palmar interossei, generally thought to insert only onto the extensor apparatus, could also insert onto bone and onto the volar plate. Classic teaching is that all dorsal interossei (except the third) have two heads and that all palmar interossei have only one head. In this study, however, 38 percent of the palmar interossei and 75 percent of the dorsal interossei had more than one head. The complexity of the interossei is apparent when as many as three different muscle heads are present, each with a different distal destination.